Drained cakes, washing

To a chromatographic column, packed with 6.67 g of charcoal ("Nuchar C") with layers of sea sand at either end, 75 ml of acetone was added to wet the carbon. The column was heated to 40°C, and 25 ml of acetone was drained off. A solution of 20 g of dry crude dehydrocholic acid in 500 ml of acetone was poured into a reservoir atop the column and maintained in this reservoir at 40°C. This solution was then allowed to drop through the column at a constant rate over a 3-hour period. The column was then washed with 250 ml of acetone flowing through the column at a constant rate over a 1-hour-period at 40°C. The column effluent and wash acetone were combined and concentrated to a residual volume of about 100 ml which resulted in the formation of a thick slurry. The slurry was cooled with stirring at 0° to 5°C and aged for 30 min at this temperature. The slurry was filtered and the filter cake washed with cold acetone. The filter cake of U.S.P. dehydrocholic acid was sucked partially dry on the filter and then dried at 110°C for 3 hours. 

Drained with cake in place after differential pressure reaches a predetermined limit Filled with wash liquid and the cake washed Drained... 

Figure 9.2 Concentration ration vs time or wash ratio. Curve (a), drained cake curve (b), saturated cake...

With the cake washed and adequately drained (using compressed air as necessary to remove the last traces of liquid), the filter press would be opened from the queen plate inwards, and the cake in each compartment be discharged into a collection trough or screw conveyor below the filter. Once every cake was discharged, and the filter media washed, then the filter would be closed and the cycle repeated. 

For the purpose of washing, the filter cake on the funnel is covered with ice water. After being allowed to remain in contact for a few seconds, the liquid is quickly drained under reduced pressure. The second portion of washing water should no longer be acid to Congo red. 

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